The invention relates to a method for producing patterned coatings on a molding and to a device for implementing the method. The molding in question is in particular a planar or three-dimensional circuit carrier, composed of an insulating material, which is provided with a patterned metallic coating, more particularly a conductor track pattern. The invention further relates to a device for implementing the method.
In the case of subtractive methods for producing planar circuit carriers (printed circuit boards), the conductor track structure comes about through the partial removal of metallization which is applied beforehand to the circuit carrier. In the case of additive methods, the conductor track structure is applied by the controlled deposition of metallization on the circuit carrier.
Planar circuit carriers (printed circuit boards) usually consist of an electrically insulating material. A customary insulating material is fiber-reinforced plastic (FR4). The conductor track structures on printed circuit boards are produced photolithographically from a thin metallization layer, made in particular of copper, as follows:
A thin layer of light-sensitive photoresist is applied to the surface of the printed circuit board, which at this stage is fully metallized. Depending on the photoresist used, the exposure of the photoresist through a mask with the desired pattern leaves either the exposed or the unexposed portions of the photoresist soluble in a developer solution, and they are removed. If the printed circuit board thus treated is introduced into a suitable etching solution (e.g., an aqueous solution of iron(III) chloride or sodium persulfate), only the photoresist-free region of the metallized surface is removed by the etching solution; the regions covered by the photoresist are retained, since the photoresist is resistant to the etching solution.
These subtractive, wet-chemical methods are subject to restrictions from standpoints of environmental protection. Moreover, the subtractive, wet-chemical methods can be carried out virtually only with printed circuit boards made of FR4 material. Plastics are not among the materials contemplated, since the additives present in the plastics become unstable due to the wet-chemical process steps, and the additives in solution in the baths alter the properties of the metallization. A further factor is that circuit carriers which are not planar, but instead are three-dimensional, cannot be economically produced by subtractive, wet-chemical methods.
In the case of injection-molded three-dimensional circuit carriers (molded interconnect devices, MIDs), however, conductor track structures can nevertheless be produced on the surface of moldings made of plastic. The circuit carrier receives its three-dimensional form through the injection molding operation, and the conductor track structures are usually applied additively, by chemical or electrochemical means, to the surface. For the molding, essentially high-temperature thermoplastics and construction thermoplastics are employed. The long operating time for producing the injection-molded, three-dimensional circuit carriers, however, is less well suited to the economic mass production of three-dimensional circuit carriers.
A method is known from DE 11 2012 004 940 T5 for producing a conductor track structure on a substrate, with the following steps:                forming a first metal layer on a nonconducting substrate;        deliberately removing a part of the first metal layer by laser to expose the nonconducting substrate, so as to form the first metal layer as a coated region and a noncoated region, the coated region being divided into two sections forming conductor tracks, and at least one bridge section;        forming a second metal layer on the coated region by electroplating only the coated region, using one of the sections forming the conductor tracks, and the bridge section, as electrode, and        removing the bridge section and the second metal layer formed on the bridge section. The removing can be done by controlled laser depletion. With that, the method for producing the structured conductor track is concluded. The removal step, however, can also be carried out chemically, by immersing the structured substrate into a chemical bath. Since the sections forming conductor tracks are wider than the bridge sections disposed between them, the bridge sections and the second metal layer formed thereon can be removed effectively by adjusting the immersion time, without adverse consequences for the sections forming conductor tracks.        